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Posted by HeatPro on June 03, 2008 at 10:44:29:
In Reply to: our problems - part 4 posted by Sean on June 02, 2008 at 23:34:22:
Thanks for the full explanation.
You have the most common of problems based on the almost universal ideas that:
A. The contractor has to 'make sure' the boiler is big enough, even though he hasn't a clue as to how to figure out the right size. So people have cubic heads and square feet, which are real handicaps.
B. The supplier has to make sure the sale and commissions are large enough to pay for the fishing.
C. The cast iron manufacturer has to keep on selling big boilers, because oil business is falling off, so heat loss estimation is no longer taught.
You have the smaller problem of radiation installed in 1920 before insulation was used in most houses so radiators were often sized to the width of the windows. This results in radiators far too large for today's houses, making the need for the water to only be less than 140F, which is bad for cast iron boilers as they sweat from the condensation and rust out sooner.
A boiler that can provide 150,000 btuh would heat a new house of 6000 square feet; but would be the right size if you had no insulation.
Weil has wisely advised the contractor to set the boiler up so it won't condense by running over 140F to 180F. Along with that is the waste. In effect, they eliminated the HeatManager benefit.
You would do well to have the boiler and main piping rearranged at the boiler to a loop-subloop arrangement, so the boiler can be used at the higher protective temperature, while the system and radiators need only be heated to 130F when needed by the upstairs thermostat. You have in effect, the same system requirements as if you had a floor radiant system, so it can be piped and controlled that way.
As a side note, a Multi-Aqua heat pump or ground source heat pump in the place of a boiler would have been an alternative way to heat your home at close to the same cost, considering the radiation.